The present invention relates generally to the field of optoelectronic devices such as light emitting diodes and semiconductor diode lasers and more specifically to the field of type II quantum well devices.
Fiber optic transmission of data signals across large distances is presently accomplished using a variety of laser transmitters, which are generally designed to operate in three primary wavelengths, e.g., 850 nanometers, 1.3 xcexcm, and 1.55 xcexcm. For a predetermined bandwidth, increasing the wavelength of light emitted from a laser transmitter acts to increase the distance that data and information may travel without requiring amplification. For example, in a system having a 10 gigabyte per second bandwidth, use of an 850 nanometer wavelength transmitter allows signals to be transmitted between approximately 50 to 100 meters without amplification, while the use of a transmitter in the 1.55 xcexcm regime allows transmission of signals up to approximately 2000 kilometers without amplification. Amplification of these signals (e.g., using an erbium amplifier) allows propagation of such signals even greater distances.
Long-haul fiber optic transmissions currently utilize 1.55 micrometer distributed feedback (DFB) edge emitting lasers as transmitters. Such DFB lasers are relatively expensive, and vertical cavity surface emitting lasers (VCSELs) potentially offer a lower-cost alternative to DFB edge emitting lasers.
A number of issues are presented by previous attempts to produce relatively low cost, manufacturable VCSEL lasers having emission wavelengths in the 1.55 xcexcm. For example, InP-based 1.5 micrometer VCSELs conventionally use wafer-bonding distributed Bragg reflectors (DBRs), metamorphic DBRs, or Sb-based DBRs. Such VCSELs require relatively sophisticated and challenging fabrication processes. Lasing performance of such VCSELs is also generally inferior to InP-based edge-emitting lasers.
Conventional active regions for 1.55 xcexcm lasers (e.g., edge-emitting lasers for use as laser pumps for Raman fiber amplifiers) are based on InGaAs or InGaAsP multiple quantum wells (MQWs) on InP substrates. Such lasers are inherently temperature-sensitive, which may not be suitable for a number of applications. It is believed that the temperature sensitivity results from several factors, including Auger recombination, carrier leakage processes, intervalence band absorption (IVBA), and temperature dependency of the material gain.
Difficulties in forming high quality DBRs on InP substrates and the temperature sensitivity of resulting activation regions has led to research in extending emission wavelengths on GaAs substrates (e.g., using highly-strained InGaAsN(Sb) quantum wells (QWs) and InGaAsxe2x80x94GaAsSb type II QWs. This research has not produced high-performance laser operation at 1.55 xcexcm.
Thus, it would be advantageous to be able to provide a laser that exhibits high performance laser operation in the 1.55 xcexcm regime using a GaAs substrate, and which may be produced relatively simply and inexpensively in comparison with conventional 1.55 xcexcm lasers. It would be particularly advantageous to provide these characteristics in a VCSEL laser.
In accordance with the present invention, GaAs based optoelectronic devices have an active region that includes electron quantum well layers of GaAsN or InGaAsN and a hole layer quantum well of GaAsSb with a type II structure. The GaAsN or InGaAsN electron quantum well layer is preferably in tensile strain and the GaAsSb hole quantum well layer is preferably in compressive strain to provide light generation at desired wavelengths. Light can be generated at relatively long wavelengths, e.g., 1.3 xcexcm or higher. A GaAs barrier layer is preferably formed adjacent to the GaAsN or InGaAsN layer.
In the devices of the invention, a multilayer semiconductor structure incorporating this active region layer is preferably epitaxially deposited on a substrate of GaAs. The thicknesses of the quantum well layers may each preferably be at least about 20 xc3x85 and less than about 50 xc3x85. The quantum well layers can be selected to provide light emission at relatively long wavelengths, e.g., in the range of 1.3 xcexcm to 3.0 xcexcm.
The device preferably includes multiple quantum wells. Such a multiple-stage quantum well device includes a substrate comprising GaAs and a GaAs barrier layer, and multiple quantum well stages each of which includes GaAsN or InGaAsN electron quantum well layers and a GaAsSb hole quantum layer, each having appropriate strain for the desired wavelength of light emission.
The present invention may be embodied in various types of optoelectronic devices including amplifiers, light emitting diodes, and edge emitting and surface emitting lasers which incorporate optical feedback to provide lasing action.
Further objects, features and advantages of the invention will be apparent from the following detailed description when taken in conjunction with the accompanying drawings.